Stabilized coating compound



Patented July 7, 1942 STABILIZED COATING COMPOUND George H. Young, Pittsburgh, Pa., assignor to Stoner-Mudge, 'Inc., a corporation of Pennsyl- Vania No Drawing. Original application October 15, 1938, Serial No. 235,164. Divided and this application May 22, 1941, Serial No. 394,625

3 Claims. (01. ze 2s) This invention relates to coating compounds capable of'iorming protective coatings upon the surfaces of other bodies, and consists specifically in a coating compound composed primarily of those resinous polymeric compounds that result from the conjoint or simultaneous polymerization of vinyl chloride and-the aliphatic esters of either or both acrylic and methacrylic acid. These thermoplastic conjoint polymers are known to the art, and usually contain a greater proportion of vinyl chloride than of ester, but my invention serves equally well when dealing with conjoint polymers that contain even a small proportion of vinyl chloride. This application is a division from an application filed October 15, 1938, Serial No. 235,164, now Patent No. 2,260,420.

Vinyl chloride is a chemical compound that corresponds to the formula CH2=CHC1. It may be derived by the action of hydrogen chloride on acetylene under the proper conditions of reaction and in the presence of any of a number of catalysts, as is well known; it'may be derived from ethylene chlorhydrin under well-known reaction conditions, by the chemical removal of the elements of water; it may be derived from ethylene dichloride or from ethylidinedichloride by wellknown reaction conditions involving the removal of hydrogen chloride. In the resinous products contemplated in this invention, vinyl chloride derived from all of these illustrative processes has beenshown to serve equally well. The use of vinyl chloride in the production of thermoplastic conjoint polymers is not new.

The aliphatic esters of acrylic acid and of methacrylic acid are well known. They may result from direct esterification' of acrylic acid or methacrylic acid with the'desired aliphaticalcohol. 'The alcohol may-be any meet the class of monohydroxy alcohols that comprise methyl alcohol, ethyl alcohol, normal and isopropyl alcohols, the severalbutyl alcohols, amyl alcohols, and so on. Further, these aliphatic esters may result from a dehydrating reaction on the corresponding alpha hydroxy esters, as is well known. In any case, the aliphatic acrylic and methacrylic esters that enterinto the conjoint polymers contemplated in my invention are equally satisfactory, regardless of the source from which they are derived. They may be generally represented by the formula CH2=CXCOOR, in which R is a-substance selected from a group consisting of the aliphatic alkyl homologous series, methyl, ethyl, normal and isopropyl, the butyls, the amyls, and the higher alkyl radicals, and X is either hydrogen or the methyl radical.

Summarizing, the conjoint polymers that are contemplated in my invention are those derived from whatever source derived. ".In the ensuing claims I use the term an acrylic acid" as inclusive of both acrylic and methacrylic acids; that is, by an acrylic acidfI meanan acid whose aliphatic esters are responsive to the formula CH2=CXCOOR, as defined above. The simultaneous polymerization may have been carried out in the presence or absence of catalysts, with or without the action of actinic light, and at normal, reduced, or elevated temperatures. The resulting thermoplastic conjoint resinous polymers, suitably dispersed in the usual ketone or lower ester solvents, thinned with the usual aromatic diluents, and containing varying proportions of added plasticizers ofv the phthalate, phosphate, citrate, sebacate, or succinate ester types, are the resinous compounds in the coating compositions which my invention contemplates.

My invention consists in the addition to such a resinous polymeric compound as those specified of a substance that will serve to impart thermal stability to a film consisting primarily of that compound. A film of the resinous copolymer of vinyl chloride and acrylate, lacking the modifying addition of my invention, will, when deposited upon metal, tend to decompose at relatively low temperatures. .While the specific decomposition temperatures vary somewhat from metal to metal, if the film be as heavy as is usual for films of this nature (exceeding 5 milligrams per square inch), the actual temperatures upon particular metals'will be found to. be as follows:

Tin plate; 335-340" F. Iron 310315 F. Zinc 290-295 F. Copper 340-350" F.

In general, it is then necessary, when dealing with these substances, so to control the baking temperature-that the temperature of decomposition be not attained. It will be obvious that this may require specialadjustment of baking or force-drying equipment, depending upon the metal that is being coated at a particular time. Furthermore, in baking a coated metal object which itself is constructed from a plurality of metals, the baking temperature, correctly adjusted for one of the metals, may be incorrect for another, with the result either that the coat ing is decomposed upon that other metal (because the baking temperature has been too high), or that the coating is insufliciently adherent to that other metal (because the baking temperature has been too low). It is frequently true that the temperature of maximum adhesion to a particular metal lies above the temperature of thermal decomposition. In such ways the application of coatings containing these thermally unstable resins is limited.

It is, therefore, a matter of desirability, and

specifically my object herein, so to increase the thermal stability of the resinousfilm compounded of polymeric "vinyl chloride and acrylate that, when spread upon such metals as those named or upon other metals or materials, it will endure greatly increased gloss, toughness, and resistance .to abrasion, moisture, atmospheric degradation,

Y and other corrosive influences.

temperatures substantially higher than those noted without undergoing decomposition,

In United States Patent'2,'130,9'24, for the joint invention of Arthur W. Johnson and myself, description is given of a type of thermal stabilizers for, the resinous polymers and copolymers, ,de-

rived from vinyl chloride and vinyl estersknownu Generally stated, the

commercially as Vinylite. resin-type substance with which we there were concerned consisted of any polymer, co-polymer, or polymeric mixture of the compound corresDondingtO theformula HCHz=CHX, in which X may be a halogen, the hydroxyl group, acetoxyl, propionoxyl, orin general any menocarboxylic .acyloxyl group; and, specifically, we found suited to our purpose those resinousproducts resulting from the simultaneous polymerization of vinyl chloride and vinyl acetate. ,The type of thermal stabilizer that we there described was a tar base, consisting of the 1 higher pyridine base homologs .boilingabove 240 C. at atmospheric pressure. ,In LettersrPatentof the United States No, 2,169,717, granted August 15, 1939, I havedescribed another class of thermal stabilizers for the resinous vinyl polymers, consisting of the quinoline and isoquinoline alkaloid bases, and particularly the cinchona alkaloid bases. In Letters Patent of the United States No. 2,208,216,

granted July 16,1940, the joint inventors; of

whom I am 'one,-claim a' broader field of invenchain substituents and that have atleast one r double bondconjugated with respect to a doublebonded nitrogen in the parent heterocyclicring system, an applied coating of the mixture possesses greatly increased thermal stability. 'Ihe ring substituted nitrogen bases containing conjugated double-bond systems so added may be used either in the form of their pure compounds or as mixed concentrates, fractionated cuts,- or basic residues derived from their synthetic preparation; or by extraction from heterocyclic'nitrogen bases containing natural products. I have found that this increase in thermal stability is noticeable upon theaddition of even a trace of the above type of stabilizer, and for practical utilization a quantity of stabilizer notexceeding 4 per cent of the weightofythe resinous conjoint polymeric compound serves to impart such stability that films deposited from the thermally stabilized coating composition can be baked at temperatures exceeding 365-375? F. or higher without suffering any thermal decomposition. In the typical formulations to bedescribed below I have usually specified that the stabilizer concentration be 1 per cent of the weight of the resinous conjoint polymeric compound. Concentrations of stabilizer in this range or even lower I have found experimentally'to yield stabilizedsolutions that can be baked at such temperature on most metals as to develop maximum adhesion without any thermal decomposition; and the coating possesses Furthermore, with such stabilized coating composition it is possible to coat objects made from a plurality of dissimilar metals and thereafter to bake the coated object at a temperature such as to insure maximum adhesion to the most recalcitrant of the metals without suffering thermal decomposition on the other metals in the object.

. I have described the type of heterocyclic nitrogen-ba'se stabilizers contemplated in my invention, in a general way. Specifically, I mean compounds of the pyridine, quinoline, and isoquiholinetype, of the acridine type, of the pyrazlne type, of the pyrazole type, of-thethiopyrazole type, or (in general) heterocyclic bases containing at least one double-bonded ring nitrogen conjugated with a double bond outside the'parent a ring. Thus, I have found that the tar bases, or; higher-pyridine base homologs, boiling above 240 C. at atmospheric pressure, that occur naturally in coal tar, natural asphalts, water-gas pitch, bonepitch, and other tarry materials, will serve. I am able to add these tar bases either as isolated products, in the form of a. purified pitchy wax containing the bases, or in the form, of the crude pitch. Similarly, I have found that any compound selected from the class known as the quinoline and isoquinoline alkaloid bases, and particularly from the cinchona alkaloid bases. will serve. The quinoline and isoquinoline alkaloid bases constitute a particular sub-class within the general class of heterocyclic nitrogen bases which I have found to serve as thermal stabilizers, Thus; I have employed with success isoquinine,

I hydroquinine, quinidine, cinchonine, cinchonidine, quinoidine, cinchona febrifuge, and crude apoquinine bases. I have found none that is not serviceable to achieve thermal stabilization, and myexperimentation indicates that all of the cinchona alkaloids, pure and impure, single and mixed, and their intermediate products of controlled decomposition by acid, such as quinicine,

cinchonatoxine, isoquinotoxine, and the like, are so serviceable. Finally, I have demonstrated that other miscellaneous heterocyclic :bases, responding to the limitationsdefirmd above under my generalized description of the class of nitrogenbase stabilizers, are also serviceable. Thus, Ihave employed with success tripyridyl, isophrophthalone, alpha-pyridyl-o-hydroxy phenyl ethlye'ne, stilbazole, alpha-pyridyl furyl ethylene, alpha- ,benzo-pyridyl-o-p-dihydroxy phenyl ethylene, and alpha-pyrazyl o-hydroxy-phenyl ethylene.

.I have found no compound responding to the generalized formula which I give below that is not, 1n greater or less degree, serviceable.

The general formula for the type of stabilizing compounds of the invention is as follows:

In this formula N is nitrogen; X may be any trior tetra-valent element capable of entering into a double-bonded system, and typically may be carbon or nitrogen; Y may be any di-, tri-, or tetrawalent element capable of entering into a double-bonded system together with X, and typically may be carbon, nitrogen, or oxygen. R, R, R' and R""v may be simply hydrogen, or

any other aliphatic or aromatic hydrocarbon radical; similarly R and RT, and R' and R" may be joined together by chemical bonds to form a condensed ri'ngsystem; also R'' and Y maybe joined together toform a condensed ring system except in the special case when Y is oxygen. FurthenA, B, D, E," and F. typically may be'carbon atoms," or one or more maybe another element, such as nitrogen, capable of entering into a ring system and of bonding to side chains shown in the above generalized formula as R, R", R' and R"". In a specialv case, oxygen or sulphur may be a member of the ring, in which case there will be no attached side group on that atom.

Specific examples (1) To 100 grams of the resinous copolymer of vinyl chloride and acrylate described above are added 2 grams of technical quinoline, and the whole is dispersed in a suitable solvent mixture Consisting of 4 parts of mesityl oxide and 1 part of isophorone. This stabilized coating compound may be spread upon tin-plate, for example, and thereafter baked at temperatures approximating 400 F. without noticeable thermal decomposition.

(2) To 100 grams of the resinous copolymer of vinyl chloride and acrylate described above is added 1 gram of a coal tar pitch containing at least one tar base boiling above 240 C. at atmospheric pressure, and the whole is dispersed in a typical solvent mixture consisting of 4 parts of mesityl oxide, 1 part of xylene, and part of dibutyl phthalate, the total concentration of solids being typically 12 per cent of the weight of the Whole. This stabilized coating compound may be spread upon tinplate, for example, and thereafter baked at temperatures approximating 400 F, without noticeable thermal decomposition.

(3) To 100 grams of the resinous copolymer of vinyl chloride and acrylate described above are added 2 grams of natural asphalt, and the Whole is dispersed in a solvent mixture consisting of 2 parts of mesityl oxide, 2 parts of isophorone, 1 part of hiflash naphtha, and /5 part of dibutyl cellosolve phthalate, the total concentration of solids being typically per cent of the weight of the whole. This stabilized coating compound may be spread upon tinplate, for example, and thereafter baked at temperatures approximating 400 F. without noticeable thermal decomposition.

(4) To 100 grams of the resinous copolymer of vinyl chloride and acrylate described above are added 4 grams of tar wax, being a waxy commercial extract of the higher tar bases occurring in coal tar pitch. The whole is then dispersed in a solvent mixture consisting of 5 parts of mesityl oxide and part of liquid chlorinated diphenyl, the total concentration of solids being typically per cent of the weight of the whole. This stabilized coating compound may be spread upon tinplate, for example, and thereafter baked at temperatures approximating 385 F. without noticeable thermal decomposition,

(5) To 100 grams of the resinous copolymer of vinyl chloride and acrylate described above is added 1 gram of water-gas pitch, and the whole is brought into solution in a suitable solvent mixture such as that described in Example 4. This stabilized coating compound may be spread upon iron, for example, and thereafter baked at temperatures approximating 345 F. without noticeable thermal decomposition.

.(6) To 100 grams of theresinous copolymerof vinyl chloride and acrylate described above are added 5 grams of coal tar pitch, and the whole is brought. into solution in: a solvent mixture which" consists" "of 3'partsj of mesityl oxide, 1 part'o'f' is'ophorone, 1- part of methyl normal propyl ketone,"- /2 part of hifla'sh' naphtha, and /5 part of tricresyl phosphate. The total concentration of solids may be typically 15 per cent of the whole. This stabilized coating compound may be spread upon tinplate, for example, and

- thereafter baked at temperatures approximating trations. If crude pitches or pitch-derived waxes be employed they should be used in proportion to their content in cyclic nitrogen-base compounds. It may be explained that in the case of crude pitch, and pitch-derived waxes, a large proportion of the content constitutes for my purpose merely a pitchy diluent for the tar base or bases supplied to the coating. For reasons of availability, however, it may under certain circumstances be desirable to utilize a crude pitch or pitch-derived wax, rather than to add technical quinoline or other cyclic nitrogen bases in separated or purified condition.

As an alternative to admixture-of the thermal stabilizing material to the resin in solution, it may in any of its forms be milled in with the solid resin. Quantitatively there is no fixed upper limit to the percentage inclusion of the thermal stabilizer with the resin. Within reasonable limits,

it is a fact that the increase in thermal stability attendant upon its use is proportional to the amount of stabilizer added. There are, of course, practical limits to the inclusion of the stabilizer in any of its forms. Thus, it is obvious that the coal-tar pitch, for example, should not be added in such large proportion that the coating becomes a pitchy coating rather than a resin film, and it is equally true that there would be no advantage in attempting to carry the endurable temperature to such point that the thermal stabilizing agent would itself decompose.

Having described fully my discovery, and having shown the advantages attendant with its use,

I claim as my invention:

1. A thermally stabilized coating compound consisting of a conjoint polymer derived from the simultaneous polymerization of vinyl chloride and an ester responding to the formula CH2: CXCOOR, in which X is a member of the group consisting of hydrogen and the methyl radical, and R is a member of the group consisting of the ethyl, methyl, propyl, butyl, and higher homologous alkyl radicals, and a pitch containing one tar base boiling above 240 C. at atmospheric pressure, such tar base being present in a ratio not to exceed 4 parts of tar base to parts of the first named substance.

2. A thermally stabilized coating compound consisting of a conjoint polymer derived from the simultaneous polymerization of vinyl chloride and an ester responding to the formula CH2: CXCOOR, in which X is a member of the group consisting of hydrogen and the methyl radical, and R is a member of the group consisting of the ethyl, methyl, propyl, butyl, and higher homologous allgvl radicals, and a. stabilizer consisting of technical quinoline, such stabilizer being present in a. ratio not to exceed 4 parts of quinoline to 100 parts of the first named substance.

3. A thermally stabilized coating compound consisting of a conjoint polymer derived from the simultaneous polymerization of vinyl chloride and methyl acrylate, and a. stabilizer consisting of a pitch containing at least one ,tar base boil n above 240 C. at atmospheric pressure, such tar base being present in a ratio not to exceed 4 parts of tar base to 100 parts of the first named substance, the whole being dispersed in a solvent.

' GEORGE H. YOUNG. 

